1. Field of the Invention
The invention relates to a belt grinding machine with an abrasive layer and a support layer for transmitting drive power onto the abrasive layer.
2. Description of the Related Art
It is known to employ an endless belt guided about at least two rollers in belt grinding machines, wherein at least one of the rollers is being driven. The abrasive layer is positioned externally, i.e., on the side facing away from the rollers while the support layer rests on the rollers. When the rollers are now rotated, the support layer is entrained and thus also the abrasive layer on the external side of the belt. In general, the inner side of one of the runs of the belt has positioned thereat a pressing shoe with which the moving abrasive belt is forced against the surface to be ground in order to provide a certain grinding pressure.
Such abrasive belts are used preferably for grinding plane surfaces. Belt grinding machines can be in the form of portable hand-held tools or can also be stationary tools.
During the grinding process grinding dust is formed which causes certain problems. On the one hand, the grinding dust causes a certain environmental impact which may result in health problems for the person operating the belt grinding machine. On the other hand, the grinding dust also clogs the abrasive layer so that the effectiveness of the abrasive layer is reduced. Accordingly, the abrasive belt in some cases has a service life which is significantly smaller than to be expected based on wear of the abrasive layer.
It has therefore already been suggested to remove the grinding dust by a suction action from the abrasive belt. For this purpose, the belt grinding machine, in the area of one deflecting roller, is provided with a suction device which acts on the external side of the abrasive belt and is designed to remove by suction the grinding dust from the surface of the abrasive layer. The effectiveness of such a suction device is however limited.
It is an object of the present invention to improve the grinding dust removal on abrasive belts.
In accordance with the present invention, this is achieved in that the abrasive layer is configured to allow particle flow therethrough, in that between the abrasive layer and the support layer an intermediate layer is arranged which is configured to allow particle flow, and in that the support layer is also configured to allow particle flow.
It is possible to provide a removal device operating by suction on the inner side of the abrasive belt which then substantially sucks the grinding dust through the abrasive belt. The grinding dust (grinding particles) can thus be removed at the location where it is generated, i.e., it does not stay or stays only for a very short time period on the surface of the abrasive layer. The particle flow, i.e., the grinding dust which is transported by air flow through the abrasive belt, penetrates first the abrasive layer. For this purpose, different possibilities are provided which will be discussed in more detail in the following. Below the abrasive layer an intermediate layer is arranged which is also configured to allow passage of grinding dust (grinding particles). In this intermediate layer, the grinding dust has the possibility to select a path which is no longer perpendicular to the grinding plane. The grinding dust can move, if necessary, also parallel to the abrasive layer. This makes it possible for the particles to penetrate the support layer at a suitable location, wherein the support layer is also configured to allow particle flow therethrough. Accordingly, it is no longer necessary that at the time of removal by suction during the grinding process an opening provided in the abrasive layer is positioned exactly aligned with a suction opening. Instead, the location and arrangement of a suction device within the belt grinding machine and within certain surface areas of the abrasive belt can be selected freely within certain limits. This has the result that the grinding dust removal functions even when the abrasive belt is moving, i.e., the abrasive layer is moving across the surface to the ground. For example, the corresponding suction device can be arranged behind the pressing shoe in the running direction of the abrasive belt or the pressing shoe can be provided with corresponding suction openings. As a result of the abrasive belt being permanently exposed to the suction action, an excellent possibility is provided to transport the grinding dust away form the abrasive surface. The service life of the abrasive belt is increased accordingly; moreover, the grinding dust is not released into the surroundings and the abrasive layer will not become clogged so quickly with the grinding dust.
In this connection, it is preferred that the support layer is formed of a material which is impenetrable for particles but is provided with a plurality of holes which are substantially uniformly distributed across its surface area. Since it is possible to employ material for the support layer that is impenetrable for the particles stream, the selection of materials for the support layer is not limited. It is possible to employ the same support material as for conventional abrasive belts. The material can be selected, in particular, with respect to the strength which must be provided by the support layer. The support material should also be, in particular, resistant to tearing. Overall, it is sufficient when the combination of abrasive layer, intermediate layer, and support layer has sufficient tensile strength. Optionally, the support layer can also be formed by a part of the intermediate layer. The particle stream through the support layer is ensured in that the support has a plurality of holes which are uniformly distributed across its surface area. These holes can be provided in the form of perforations. The fact that the holes are uniformly distributed across the surface area does not mean that in all cases a regular pattern must be present. It is only required that the ratio of open surface area to remaining support layer surface area is substantially constant across the entire surface area of the support layer when surface area portions of a few square centimeters, for example, 10 cm2, or less are considered.
Preferably, the holes have a maximum spacing relative to one another which as a function of the intermediate layer is selected such that a substantially dynamic pressure-free particle flow can be generated beginning at the abrasive layer and passing through the intermediate layer and through the holes. Accordingly, the holes can have a spacing relative to one another that is the greater the easier the dust particles can flow parallel to the support layer through the intermediate layer.
Preferably, the intermediate layer is an open-pore foam. Such foam can be realized, for example, by a foamed material layer. The foamed material layer makes it possible for the dust particles to move basically in all directions. The dust can thus flow within the foamed material layer from the abrasive layer to the individual holes in the support layer.
Preferably, the intermediate layer is elastic. In addition to the function of providing a flow path for the particle flow, the intermediate layer also takes over the function of configuring the abrasive belt so as to yield to certain degree so that smoother surfaces can be obtained.
Preferably, the support layer is made of paper, fabric or film. These materials have proven successful in practice. They can transmit high tensile forces and are relatively inexpensive. The film is preferably a plastic film. It is also possible to employ a non-woven or other material of less tensile-strength when the abrasive belt otherwise overall is of great tensile strength or can operate in a different way.
Preferably, the abrasive layer has an abrasive particle support comprised of a material which is impenetrable for a particle flow therethrough but has an arrangement of a plurality of perforations over its surface area. In this connection, basically the same considerations as for the support layer apply. The perforations are arranged such that the dust which is produced during grinding must not travel large distances on the surface of the abrasive layer but can be sucked relatively quickly through the next perforation into the interior. The perforations must not be provided in a certain pattern even though this facilitates their manufacture. The use of a material which is impenetrable to a particle flow has the advantage that for the abrasive particle support materials can be also used which have been proven successful in practice. The permeability for the particle flow is provided by the perforations.
Preferably, the perforations have a diameter in the range of 0.5 to 5 mm and neighboring perforations have a maximum spacing to one another of 20 mm, wherein the maximum spacing of the edge to the next perforation is 15 mm. Conventionally, the spacings between neighboring perforations and the spacing of the edge at each location next to a perforation are of even smaller values, for example, in the range of magnitude of 10 mm. This provides relatively short travel distances which must be traveled by the grinding dust on the surface of the abrasive belt before it can be sucked into the next perforation.
Preferably, the abrasive particle support is formed of paper, fabric, or film. The film may be particularly a plastic film. On these materials, abrasive particles, for example, the abrasive grain, can be easily attached.
In an alternative embodiment it is proposed that the abrasive layer is formed as an abrasive grate. With such an abrasive grate it is possible to obtain especially fine grinding results. In the case of an abrasive grate, the particle flow can penetrate through the openings which are formed by the individual mesh openings of the grate.